Great post, wish the forums were full of more people like Possessed.
All of this advice is great, the most important points: keybinds, macros, mouse turning, practice. Don't let anyone tell you that clicking is comparable to keybinds, it's just not true. When you learn how to keybind your reactions will be much, much faster. You need to give it time and build muscle memory. Also, find like-minded players. At times the community can seem really toxic and the balance of the game can be frustrating, finding chill people to play with and have fun makes a world of difference.
Advice on keybinding: start by changing turn left/right to strafe left/right and then keybind your rotational abilities to comfortable keys (try starting with your main 4-5 abilities and working your way up as you get used to each new keybind). Also, a mouse with extra side buttons is really helpful for binding cooldowns or escapes. I love the mouse wheel for interrupts. Learn to love the shift modifiers and look in to help / harm macros if you ever decide to play a healer or more support oriented spec.
One last point:
focus macros or even better @arena1,2,3 macros will make your life much easier when it comes to CC'ing healers.
The addon GladiatorlosSA is useful when you are learning how to play arena. It announces important enemy spells and until you learn visual/sound cues it is extremely helpful. I recommend disabling it everywhere except arena - otherwise you get spammed.
More addons: Interruptbar (might be called Omnibar now), also want to point out tidyplates again - probably one of the only addons I can't live without (the other being MikScrollingBattleText)
Oh! and mouseover macros are a godsend.